By the amazingly low standards of the ITV 'Marple' series, this one is not bad. On the message board, the contributor 'Last picture show' points out, quite correctly, that the plot does not in fact make sense. However, I failed to notice this when watching and found the ending satisfying at the time.
Despite disfiguring the original book for insufficient reasons, this version did hold my interest. One factor was Juliet Stevenson and Denis Lawson's performances. The tragedy of Gwenda's life comes over very well. Another plus point is Julian Rhind-Tutt as Dr Calgary. He makes the part amusing without descending to silliness. In fact, everyone in the production seems to take it fairly seriously. This is a relief after the facetiousness of other episodes in this series.
As ever, there are anachronisms. We appear, as usual, to be in the early 1950s and the series designer takes great pains over this. However, it is all thrown away when the script includes phrases such as 'leg-over merchant', 'move on' (in the sense of getting over a tragedy) and - most glaringly of all - 'scam' (this last one from the mouth of Miss Marple). 'Scam' is first recorded in America in the 1960s. I doubt that it reached England before the 70s, and even then, elderly ladies like Miss Marple would hardly be likely to use it. (On the other hand, we also never thought that Miss Marple was a safe-breaker until this film!) There are more anachronisms with some of the hair and costumes.
Despite the defects, this one is worth watching.